Implantation of medical devices, such as pacemakers, neurostimulators, implanted drug pumps, leads, catheters, etc, has been associated with adverse consequences, such as formation of scar tissue surrounding the implant and infection due to bacteria introduced during implantation. Attempts to prevent or control such adverse reactions have included administration of drugs, completely separate from the intended primary therapy of the implanted medical device. In some cases, systemically administered drugs, e.g. orally, intravenously, or intramuscularly administered drugs, have proven effective in treating complications due to medical device implantation. In other cases, systemic delivery has been ineffective due to, e.g., pharmacokinetic or pharmacodynamic characteristics of the drug, the location of the implanted device, or side effects of the drug. To increase effectiveness in these situations, some implanted devices have been modified to elute the drug into the surrounding tissues.
One common way of providing local drug elution is to dispose a polymer layer on the implantable medical device and embed the drug into the polymer during manufacturing. When hydrated after implant, the drug diffuses out of the polymer into surrounding tissue. Various methods of impregnating polymers with drugs have been used, including mixing the drug into the melted polymer prior to processing (e.g. molding or extrusion), and diffusing the drug into a finished polymer component using chemicals to swell the polymer for rapid loading. In some cases, the implantable medical device (IMD) is made from a polymer that is compatible with the drug, and the drug can be loaded directly into the device.
However, incorporation of a therapeutic agent into or onto polymeric material of an implantable medical device may have several drawbacks. For example, the therapeutic agent may not be compatible with sterilization techniques typically employed with medical device.